It is known that organic polymers each containing in the molecule thereof at least one reactive silicon group are crosslinked by the formation of a siloxane bond which follows a hydrolysis reaction of the reactive silicon group or some other reaction on the basis of moisture or the like at room temperature, so that a rubbery cured article is obtained. The reactive silicon group referred to in the present invention means silicon-containing group(s) which have a hydroxyl group or hydrolyzable group bonded to a silicon atom and can be crosslinked by the formation of a siloxane bond.
Out of these polymers having a reactive silicon group, organic polymers having a main chain made of a polyoxyalkylene polymer or isobutylene polymer have already been produced industrially, and have widely been used in articles such as a sealant, an adhesive, and a paint (Patent Documents 1 and 2).
In the case that the polymers are each used as a sealant, an adhesive or a paint, the formulation thereof is a nontransparent formulation into which calcium carbonate, clay, talc, pigment or the like is incorporated in almost all cases. When an organic polymer having a reactive silicon group is used as a sealant for building or an industrial sealant, it is necessary that the polymer matches with a substrate around it and thus it is necessary to prepare the color species of the sealant the number of which is equal to that of colors of substrates. Thus, there is a drawback that various kinds thereof are required to be in stock. However, a transparent and colorless sealant can match with any wall color so that this drawback can be overcome.
When the polymer is used as an adhesive, the adhesive itself is not seen from the outside; however, when the adhesive is applied in a large amount or an inconvenience is caused in constructing execution, the adhesive is forced out from the jointed portions. Thus, if the adhesive is a colored adhesive, there arises a problem that the external appearance deteriorates. About transparent and colorless adhesives, a forced-out portion thereof is not inconspicuous so that the external appearance is not disfigured. From such a background, a transparent composition is preferable in some cases. A curable composition excellent in transparency wherein an organic polymer having a reactive silicon group is used are known (Patent Documents 3, 4, 5, 6 and 7).
In many of these compositions, an organotin-based catalyst having a carbon-tin bond, such as dilaurate dibutyltin or diacetylacetonate dibutyltin, is widely used as a silanol curing catalyst. In recent years, however, about organotin-based compounds, the toxicity thereof has been pointed out. Thus, organotin-free catalysts are required to be developed. As such organotin-free catalysts, suggested are catalyst systems wherein various metal carboxylates, or a combination of a carboxylic acid and an amine compound is used (Patent Documents 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, and 18).    Patent Document 1: JP-A-52-73998    Patent Document 2: JP-A-63-6041    Patent Document 3: Japanese Patent No. 3435351    Patent Document 4: JP-A-2002-37969    Patent Document 5: JP-A-2003-313421    Patent Document 6: JP-A-2004-277751    Patent Document 7: JP-A-2004-292621    Patent Document 8: JP-A-55-9669    Patent Document 9: Japanese Patent No. 3062626    Patent Document 10: JP-A-5-117519    Patent Document 11: JP-A-6-322251    Patent Document 12: JP-A-9-12860    Patent Document 13: JP-A-11-116686    Patent Document 14: WO 00-56817    Patent Document 15: WO 04-31300    Patent Document 16: JP-A-2000-345054    Patent Document 17: JP-A-2002-285018    Patent Document 18: JP-A-2004-189946